Process of impregnating steel with copper-aluminum



p 1958 G. A. SAMUEL 2,851,377

PROCESSOF IMPREGNATIIIG STEEL WITH COPPER-ALUMIN Filed Dc. 28. 1955 INVENTOR Gearye A. Jmuefl United States Patent ii?ice PROCESS OF IMPREGNATING STEEL WITH COPPER-ALUMINUM George A. Samuel, White Plains, N. Y., assignor to Metal Diffusions, Inc, Philadelphia, Pa., a corporation of New Jersey Application December 28, 1955, Serial N 0. 555,828 1 Claim. (Cl. 117-130) The present invention relates to coating with copper of metal objects, preferably of low carbon, medium carbon or high carbon steel, tool steel, alloy steel or heat resisting steel.

A purpose of the invention is to impregnate metal objects with copper more rapidly than has heretofore been possible.

A further purpose is to obtain more uniform penetration of copper on steel objects of irregular contour, eliminating the tendency to build up on raised portions, and eliminating the difficulty through lack of throwing power, which are encountered in electroplating copper.

Further purposes appear in the specification and in the claim.

In the drawing I have chosen to illustrate one only of the numerous embodiments in which my invention may appear, selecting the forms shown from the standpoints of convenience in illustration, satisfactory operation and clear demonstration of the principles involved.

The figure illustrates, in central vertical section, equipment useful in applying the invention.

Describing in illustration but not in limitation and referring to the drawing:

Copper coatings are frequently applied on metal parts including nonferrous metals, but especially on iron and steel. When reference is made to steel it is intended to indicate low carbon, medium-carbon and high carbon grades of plain carbon steel, of low alloy steel, of high alloy steel, of tool steel and of heat resisting steel.

Flash coatings with copper are applied by dipping steel objects in a solution of a copper salt and electroplating is very widely used to apply copper coatings on steel and the like. These coatings, While adherent, do not fuse into the base metal, and may be comparatively easily broken away from the base metal under conditions of impact and abrasion.

Coatings applied by electroplating are also subject to limitations in the throwing power so that the resulting coating may not be entirely uniform, for example building up on certain projections, and tending to slight remote recesses.

The present invention is concerned with obtaining uniform and extremely ductile and adherent coatings of copper on base metal especially steel, at low cost and with improved penetration.

The operation is carried on in a molten salt bath maintained at elevated temperature, and preferably at about the melting point of copper, and below the temperature at which the metal object would be damaged.

The process of the invention produces a copper impregnation which is very uniform and extremely firmly attached, since diffusion takes place, and which does not depend on throwing power in obtaining the deposit.

The copper coating of the invention in the case of steel is carried out at temperatures between 1650 and 2150 F. and preferably at temperatures between 1850 and 2050 F.

2,851,377 Patented Sept. 9, 1958 In the drawing, I illustrate a container 20 suitably of steel, or heat resisting alloy, or refractory, heated in any suitable way, electrically or by fuel, and stirred in any suitable way, as by electric current or by mechanical stirring. The furnace contains a molten salt bath 21. In contact with the molten salt bath an excess of copper 22 is placed in one embodiment of the invention, preferably in the form of finely divided copper particles or molten copper.

The bath is suitably protected by a cover 23, and an inert gas is desirably introduced through a pipe 24 in the cover. The inert gas may be nitrogen, carbon monoxide, helium or argon. If proper precautions are taken, ammonium or hydrogen may be used. The work 25 is conveniently supported by hooks 26 from a grill 27 extending across above the bath. The work can of course be handled in baskets or conveyors.

Example I The following composition is heated slowly to 1900 P. so that the Water is given off:

Parts by weight In this example no additional copper is necessary, although it can be added to replenish the bath. There is very little fume and the salt remains very liquid.

Low carbon steel chain is inserted into the bath. A flash coating takes place almostimmediately and after an hours immersion a very even, uniform penetration. occurs. Precautions should preferably be taken to move the chain during coating so that points of contact between the links will not interfere with the uniformity of coating.

One unusual feature of the invention is that the bath cleans the work, and rusty chain was cleaned and very uniformly copper coated.

Low carbon steel sheet was inserted in the bath. It received a flash coating almost immediately and a uniform coating of appreciable thickness after an hour. After removing from the bath and cooling to room temperature the sheet was bent at right angles in a sharp bend without any evidence of separation between the copper coating and the steel.

The experiment was repeated using high carbon tool steel hacksaw blades. The blades received a uniform coating after an hour though there appeared to be less penetration than in the case of low carbon steel.

Where a lower melting point of the salt bath is desired, another salt such as sodium chloride is preferably added.

halide.

Example 2 The procedure of Example 1 was repeated with the following additions: i

Parts by weight Copper powder through a mesh per linear inch screen 0.5

It is found that this addition of metallic copper speeds up the reaction and metallic copper is preferably maintained in excess in contact with the bath.

In addition to the experiments referred to in Example 1 which were repeated here with similar results but somewhat increased speed, round low carbon steel wire was run through the molten salt bath of Example 2 Without contacting the metallic copper at the bottom. A uniform copper coating was obtained and the wire was hammered down flat without any indication of separation of the copper which remained very ductile.

Example 3 The procedure of Example 2 was followed adding in addition the following: 7

Parts by weight Silicon-titanium powder (47% titanium) 0.12

It was found that the addition of this deoxidizing agent did not greatly increase the speed of reaction, and judging from the results obtained by repeating the procedure of Examples 1 and 2 the deoxidizing agent is unnecessary under these conditions.

Example 4 The procedure of Example 1 was carried out operating at a temperature just above the melting point of copper. It was found that there was no'special advantage in operating above the melting. point of copper.

Example 5 The following bath was made up and heated slowly to 2000 F.:

Parts by weight Boric acid 2O Metallic copper powder as above 1 Previously cleaned steel articles of various carbon contents were immersed in the bath. As the copper completely dissolved additional copper was added as required.

A flash copper coating formed on the steel articles almost immediately and a very adherent heavy layer was obtained on low carbon steel in the course of an hour, the layer being less thick on high carbon steel.

It was found that the objects could be quenched satisfactorily from the salt bath.

Other boron compounds may be used instead of or with boric acid, examples being borax and sodium metaborate.

Example 6 Example 2 was repeated with the following addition to the bath:

Parts by weigh Aluminum chloride, AlCl .6H O 0.6

It has been found that the. proportion of aluminum to copper can be varied by introducing varying content of aluminum salts and copper salts in the bath.

in general I find that the content of copper compound added to the salt bath may vary between 0.1 percent and 50 percent or more by weight,.and the quantity of aluminum salt added may vary between 0.1 percent and 50 percent or more by weight, it being evident of course that in many instances it may be desirable to prevent separation of a. distinct phase or formation of a very pasty mass. Excess of copper in contact with the bath is desirable and in some cases excess of aluminum in contact with the bathv is desirable.

The base of the bath will preferably be a chloride such as barium chloride, it being evident of course that other material such as sodium chloride can suitably be added to lower the melting point.

It will be evident that other salt bath bases may be used of which boric acid is one example.

Both the copper coating and the copper-aluminum coating can be performed in the temperature range from 1650 to 2150 F. as above set forth, preferably at 1850 to 2050 F.

In view of my invention and disclosure variations and modifications to meet individual whim or particular need will doubtless become evident to others skilled in the art, to obtain all or part of the benefits of my invention without copying the method shown, and I, therefore, claim all such insofar as they fall within the reasonable spirit and scope of my claim.

Having thus described my invention, what I claim as new and desire to secure by Letters Fatent is:

The method of impregnating solid steel articles with copper and aluminum, which comprises making up a molten salt bath predominantly consisting of barium chloride and containing copper halide and aluminum halide, maintaining metallic copper and metallic aluminum in contact with the molten salt bath, maintaining the temperature of the salt bath between 1650 and 2150 degrees E, and immersing the solid steel articles to be impregnated in the salt bath.

References Cited in the file of this patent UNITED STATES PATENTS 141,132 Gauduin et al. July 22, 1873 2,398,738 Gilbert Apr. 16, 1946 FOREIGN PATENTS 3,970 Great Britain 1872 OTHER REFERENCES Campbell: Salt Bath Chromizing, Journal Electrochemical Society, vol. 96, #4, October 1949, pp. 262-273. 

